This application is based on Japanese Patent Application HEI 10-329764, filed on Nov. 19, 1998, the entire contents of which are incorporated herein by reference.
a) Field of the Invention
The present invention relates to a semiconductor device and its manufacture method, and more particularly to a semiconductor device having a polycrystalline layer and its manufacture method.
b) Description of the Related Art
Polysilicon layers are used as various elements of various types of semiconductor devices. Following methods are known as manufacture methods for polysilicon layers.
(1) After an amorphous silicon layer is formed, this layer is subjected to a heat treatment for about 50 hours at a temperature of about 600xc2x0 C. to polycrystallize it. With this method, crystal growth nuclei are formed in the amorphous silicon layer at an earlier stage of the heat treatment, and crystals are grown from these growth nuclei to polycrystallize the amorphous silicon layer.
(2) After an amorphous silicon layer is formed, an energy beam such as a laser beam is applied to this layer to melt it and thereafter cool it. During the cooling process, the molten silicon layer is crystallized and a polysilicon layer is formed.
(3) A silicon layer is formed on a base substrate through chemical vapor deposition or physical vapor deposition at a temperature of about 600xc2x0 C. Since the substrate is maintained at a sufficiently high temperature, a grown silicon layer becomes a polysilicon layer.
A method of forming various types of semiconductor devices by forming a silicon layer on a glass substrate has been adopted for liquid crystal display devices and solar cells. A polycrystallized silicon layer can improve the performance of a semiconductor device more than a silicon layer of an amorphous phase. Generally, a glass substrate cannot resist a temperature higher than 600xc2x0 C., and deformation or the like occurs at such a high temperature.
The above-described method (1) requires a heat treatment temperature of about 600xc2x0 C. A number of stacking faults and twin crystals are formed in a polysilicon layer grown on a glass substrate and it is difficult to form a polysilicon layer having good crystallinity.
The above-described method (3) requires a temperature of 600xc2x0 C. or higher when the film is formed. Even if a polysilicon layer is grown on a glass substrate, crystallinity is not sufficient similar to the method (1) and it is difficult to form crystals providing a high mobility of carriers.
A remaining possibility of growing a polysilicon layer on a glass substrate is the above-described method (2). A polysilicon layer formed by utilizing laser annealing has high quality. However, the conditions of forming high quality polysilicon are restricted and very narrow. A method capable of stably forming a high quality polysilicon layer has been desired.
It is an object of the present invention to provide a method capable of manufacturing a semiconductor device with a high quality polycrystalline layer.
It is another object of the present invention to provide a semiconductor device with a high quality polycrystalline layer formed on a base substrate such as a glass substrate.
According to one aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising the steps of: preparing a base substrate; forming a first semiconductor layer on a surface of the base substrate; forming a first polycrystalline semiconductor layer by applying an energy beam to the first semiconductor layer; etching a surface layer of the first polycrystalline semiconductor layer; and after the etching step, forming a second semiconductor layer on a surface of the first polycrystalline semiconductor layer without exposing the surface of the first polycrystalline semiconductor layer to an atmospheric or environmental air.
According to another aspect of the present invention, there is provided a semiconductor device comprising: a base substrate including a glass substrate; and a polycrystalline semiconductor layer formed on the base substrate, the polycrystalline semiconductor layer having a number of grain boundaries extending from a lower surface to an upper surface of the layer and a peak of an atmospheric impurity concentration distributing in a whole area of the layer at a predetermined depth.
A polycrystalline semiconductor layer having a large crystal grain size can be formed by applying an energy beam to a semiconductor layer having a thickness of a predetermined value or smaller. The surface layer of this polycrystalline semiconductor layer is etched to expose a clean crystal surface and another semiconductor layer is formed on this clean crystal surface. By polycrystallizing the other semiconductor layer, a polycrystalline semiconductor layer can be formed which is epitaxially continuous with the underlying polycrystalline semiconductor layer.
A polycrystalline semiconductor layer made of a lamination of a plurality of semiconductor layers formed in the above manner has a crystal orientation continuous from the lower layer to the upper layer and a peak of an atmospheric impurity concentration near at interfaces between the layers.
A polycrystalline semiconductor layer of high quality can be formed on the base substrate in the manner described above. For example, a polysilicon layer having a high mobility of carriers can be formed on a glass substrate. Crystallinity can be expected to be improved, and semiconductor elements can be formed by using such a polycrystalline semiconductor layer. For example, a liquid crystal display device having integrally formed peripheral circuits and a system-on-panel semiconductor device can be formed.